Ground Test Facilities Research Articles

Real-time modular dynamic modeling for compression system of altitude ground test facilities

Modeling of a centrifugal compressor is of great significance to surge characteristics and fluid dynamics in the Altitude Ground Test Facilities (AGTF). Real-time Modular Dynamic System Greitzer (MDSG) modeling for dynamic response and simulation of the compression system is introduced. The centrifugal compressor, pipeline network, and valve are divided into pressure output type and mass flow output type for module modeling, and the two types of components alternate when the system is established. The pressure loss and thermodynamics of the system are considered. An air supply compression system of AGTF is modeled and simulated by the MDSG model. The simulation results of mass flow, pressure, and temperature are compared with the experimental results, and the error is less than 5%, which demonstrates the reliability, practicability, and universality of the MDSG model.

Hybrid time-frequency domain dual-probe coherent anti-Stokes Raman scattering for simultaneous temperature and pressure measurements in compressible flows via spectral fitting.

We demonstrate a hybrid time-frequency spectroscopic method for simultaneous temperature/pressure measurements in nonreacting compressible flows with known gas composition. Hybrid femtosecond-picosecond, pure-rotational coherent anti-Stokes Raman scattering (CARS), with two independent, time-delayed probe pulses, is deployed for single-laser-shot measurements of temperature and pressure profiles along an ∼5-mm line. The theory of dual-probe CARS is presented, along with a discussion of the iterative fitting of experimental spectra. Temperature is obtained from spectra acquired with an early, near-collision-free probe time delay (τ 1=0p s) and pressure from spectra obtained at probe delays of τ 2=150-1000p s, where collisions significantly impact the spectral profile. Unique solutions for temperature and pressure are obtained by iteratively fitting the two spectra to account for small collisional effects observed for the near zero probe delay spectrum. A dual-probe pure-rotational CARS system, in a 1D line-imaging configuration, is developed to demonstrate effectively the simultaneous temperature and pressure profiles recorded along the axial centerline of a highly underexpanded jet. The underexpanded air jet permits evaluation of this hybrid time-frequency domain approach for temperature and pressure measurements across a wide range of low-temperature-low-pressure conditions of interest in supersonic ground-test facilities. Single-laser-shot measurement precisions in both quantities and pressure measurement accuracy are systematically evaluated in the quiet zone upstream of the Mach disk. Precise thermometry approaching 1%-2% is observed in regions of high CARS signal-to-noise ratios. Pressure measurements are optimized at probe time delays where the ratio of the late probe delay to the Raman lifetime exceeds four (τ 2/τ R>4). The impact of low-temperature Raman linewidths on CARS pressure measurements is evaluated, and comparisons of CARS pressures obtained with our recent low-temperature pure-rotational Raman linewidth data and extrapolated high-temperature Q-branch linewidths are presented. Considering all measurements with τ 2/τ R≥4.0, measured pressures were on average 7.9% of the computed isentropic values with average shot-to-shot deviations representing a combination of instrument noise and fluid fluctuations of 5.0%.

Study of pressure surge during priming phase of start transient in an initially unprimed pump-fed liquid rocket engine

In this paper, transient phenomenon during start up process of a pump fed liquid rocket engine is investigated through numerical simulation. The engine studied in this work is designed such that engine systems are not wetted with propellant until the engine is commanded to start. This is achieved by positioning the valves for propellant admission at the interface of test stand/flight stage and the engine. To evaluate engine performance during start transient for such systems, unsteady flow simulation was conducted using Method of Characteristics and equations for priming. The same has been reported in this work. The results indicated a brief period of abrupt pressure rise at pump upstream after opening of the propellant admission valves, during the process of priming of engine systems at valve downstream. The peak pressure obtained was significantly higher than the propellant tank pressure as well as the steady state pump suction pressure. The transitory pressure rise was found to occur due to flow resistance at impeller inlet caused by formation of a forced vortex for orienting the flow through impeller blades during off design transient regime. The maximum pressure at pump upstream, as computed from start transient simulation, was used as a design input for pump inlet feed lines. The engine was realized and subsequently qualified in a ground test facility. Hot test data obtained for pressure and flow rate during transient regime were found to be in good agreement with the simulation results.

An anti-windup design with local sector and H2/H∞ optimization for flight environment simulation system

Flight Environment Simulation System (FESS) is an important ground test facility, which can simulate the flight environment to test the performance of the aircraft engine. Focusing on the anti-windup control of FESS in the presence of actuator (magnitude and rate) saturations, an anti-windup design method with local sector and H2/H∞ optimization is proposed. Firstly, the saturation-type static nonlinearities are separated from the dynamic nonlinear model of the actuator, and then an anti-windup architecture with static compensator is constructed. Subsequently, the integrated H2 performance and H∞ performance are used to deal with the saturation nonlinearities to reduce the system performance degradation caused by the magnitude and rate saturations. Meanwhile, the internal stability of the closed-loop system is guaranteed via local sector condition. Finally, an optimization problem based on Linear Matrix Inequalities (LMI) is developed for anti-windup design, in which internal stability, H2 performance and H∞ performance are considered. The designed anti-windup controller is applied to FESS, and the numerical simulation results verify the effectiveness of the proposed method. Furthermore, some key issues in anti-windup design are discussed.

A Multi-Cavity Iterative Modeling Method for the Exhaust Systems of Altitude Ground Test Facilities

To solve the modeling problem of altitude ground test facility (AGTF) exhaust systems, which is caused by nonlinearity along the gas path and the difficulty of ejection factor calculation, a multi-cavity iterative modeling method is presented. The components of exhaust systems, such as the exhaust diffuser and cooler, are built with a series of volumes. It overcomes the disadvantage that traditional lumped-parameter models have, whereby they cannot calculate the dynamic parameters along the gas path. The exhaust system model is built with an iterative method based on multi-cavity components, and simulations are carried out under experimental conditions. The simulation results show that the maximum error of pressure is 2 kPa in the steady state and less than 6 kPa in the transient process compared with experimental data. Closed-loop simulations are also carried out to further verify the accuracy and effectiveness of the multi-cavity iterative exhaust system modeling method.

Aerodynamic Metrologists Guide to Dynamic Force Measurement

Static aerodynamic force measurement is generally of interest in both low- and high-speed ground test facilities, but dynamic force measurement is typically associated with higher-speed facilities. This work will show that dynamic force measurement is relevant to all aerodynamic metrologists because wind tunnel system dynamics can change the force transducer’s dynamic sensitivity resulting in differences between the static and dynamic sensitivity. In addition, the field of dynamic force measurement will be introduced using realistic wind tunnel scenarios, wherein the wind tunnel system dynamics contribute to increased uncertainty in what would otherwise be considered a static force measurement. A design approach focused on estimating the dynamic response is presented to achieve measurement objectives through the use of static force measurement techniques where possible. To that end, a reduced-order model is developed to characterize the dynamic response of the system, which can serve as a predictive tool in the design process. Then, strategies for characterizing wind tunnel system dynamics to determine acceptable bandwidths wherein the static measurements may be sufficient are discussed. In the event that systems have undesirable dynamic characteristics, which cannot be avoided in the design process, two dynamic compensation techniques to correct the measured signals are discussed.

Spectral Features for Reentry Breakup Event Identification

The fragmentation of two aerospace aluminum alloys is investigated in a ground testing facility including mechanical loads as occurring due to aerodynamic forces in a real atmospheric entry event at three trajectory points. The emission spectroscopic analysis shows that these materials fail after distinct alkali metal features are observed in the spectra. The two alloys feature characteristic emissions of the different alkali metals. The presence of lithium lines that have previously been exclusively attributed to battery failure in observation campaigns may be considered as a marker for aluminum breakup. This is particularly interesting for future entry observations because it allows a new insight into the structural failure processes of the demising spacecraft. The lack of emissions of alloying elements points to these spectra being candidates for the determination of spacecraft demise. The identification of such features in ground testing will allow a more certain identification of specific breakup events.

Evaluation of Fay and Riddell formula under hypersonic flight conditions

PurposeThe Fay and Riddell (F–R) formula is an empirical equation for estimating the stagnation-point heat flux on noncatalytic and fully catalytic surfaces, based on an assumption of equilibrium. Because of its simplicity, the F–R has been used extensively for reentry flight design as well as ground test facility applications. This study aims to investigate the uncertainties of the F-R formula by considering velocity gradient, chemical species at the boundary layer edge, and the thermochemical nonequilibrium (NEQ) behind the shock layer under various hypersonic NEQ flow environments.Design/methodology/approachThe stagnation-point heat flux calculated with the F–R formula was evaluated by comparison with thermochemical NEQ calculations and existing flight experimental values.FindingsThe comparisons showed that the F–R underestimated the noncatalytic heat flux, because of the chemical composition at the surface. However, for fully catalytic heat flux, the F–R results were similar to values of surface heat flux from thermochemical NEQ calculations, because the F–R formula overestimates the diffusive heat flux. When compared with the surface heat flux results obtained from flight experimental data, the F–R overestimated the fully catalytic heat flux. The error was 50% at most.Originality/valueThe results provided guidelines for the F–R calculations under hypersonic flight conditions and for determining the approximate error range for noncatalytic and fully catalytic surfaces.

One-dimensional air temperature measurements by air resonance enhanced multiphoton Ionization thermometry (ART).

In this work, a detailed calibration study is performed to establish non-intrusive one-dimensional (1D) rovibrational temperature measurements in unseeded air, based on air resonance enhanced multiphoton ionization thermometry (ART). ART is generated by REMPI (resonance enhanced multi-photon ionization) of molecular oxygen and subsequent avalanche ionization of molecular nitrogen in a single laser pulse. ART signal, the fluorescence from the first negative band of molecular nitrogen, is directly proportional to the 2-photon transition of molecular oxygen C3Π (v = 2) ← X3Σ (v'=0), which is used to determine temperature. Experimentally, hyperfine structures of the O2 rotational branches with high temperature sensitivity are selectively excited through a frequency-doubled dye laser. Electron-avalanche ionization of N2 results in the fluorescence emissions from the first negative bands of N2 + near 390, 425, and 430nm, which are captured as a 1D line by a gated intensified camera. Post processing of the N2 + fluorescence yields a 1D thermometry line that is representative of the air temperature. It is demonstrated that the technique provides ART fluorescence of ∼5cm in length in the unseeded air, presenting an attractive thermometry solution for high-speed wind tunnels and other ground test facilities.

Rocket Sled Based High Speed Rail Track Test Facilities

The present study introduces and compares several high-speed track based ground test facilities available all over the world to simulate high-speed dynamic events for selected portions of flight trajectories. The scope of performing high speed flight-testing is addressed, which is followed by the requirements of these track based test facilities. The facilities deliver flight test articles under controlled conditions to achieve high velocity impact, acceleration, aerodynamic and other related testing for small and large test articles depending upon the requirements. Sled is designed in such a way so that it can carry the test articles like aircrafts, payloads, warheads, missiles and many other ballistic systems to achieve high velocities ranging from subsonic to hypersonic by accelerating these sleds using solid rocket motors over the rail track. Such facilities provide instrumentation for large set of trial data acquisition and offline analysis for both recovery and non- recovery (impact) trials, which makes such facilities important for test, research and evaluation purposes.
 Here, the detailed description of test facilities, which are available in many countries such as India, United States (US), Japan, United Kingdom (UK), France, and others countries based on their technical characteristics is presented. Additionally, a brief history and introduction into basic rocket sled test facility aspects, essential technical characteristics and major features to support high speed testing at these facilities as an accurate testing technique based on quality of construction and engineering design are also covered in this paper. Compilation of available or under development facilities is done in one place which provides the information about facilities’ technological gaps. The paper concludes with an explanation of the role, major capabilities and limitations of these test facilities in the present global scenario.

Development and test of a robotic arm for experiments on close proximity operations

Future spacecraft will be provided with special features to enable On-Orbit-Servicing missions. Such features include capture interfaces, proximity sensors, and algorithms for autonomous RVD (Rendezvous and Docking). The reliability standards of the space industry require all these technologies to be tested in relevant environment; to this purpose, several ground testing facilities have been built during the last years. They reproduce many aspects of the free-falling motion of a spacecraft often exploiting two technologies: robotic systems and low friction tables. The first use a virtual environment to compute the effects of the external forces and reproduce the motion of a spacecraft with a robotic arm; the second unbind vehicle mock-ups from friction effects, allowing them to experience a free motion at least in three degrees of freedom. Merging together these two types of facilities gives the possibility to further extend their capabilities.This work presents a series of tests conducted on a custom robotic arm, intended to be integrated with a low friction table. The tests focus on two main aspects: (i) the accuracy of the positioning capability and (ii) the dynamic behaviour of the robotic arm. Both aspects are directly connected with the final purpose of operating in conjunction with a vehicle floating on a low friction table. The paper also presents some improvements of the robotic arm suggested by the results of the tests to fit the requirements on the positioning accuracy. These are represented by three main achievements: (i) the accuracy is comparable with the principal navigation sensor; (ii) the vibrations are below the error of the navigation sensor, and (iii) the ability of the robotic arm in performing a capture task.

Probing spin-dependent dark matter interactions with ^6Li

CRESST is one of the most prominent direct detection experiments for dark matter particles with sub-GeV/c^2 mass. One of the advantages of the CRESST experiment is the possibility to include a large variety of nuclides in the target material used to probe dark matter interactions. In this work, we discuss in particular the interactions of dark matter particles with protons and neutrons of ^{6}Li. This is now possible thanks to new calculations on nuclear matrix elements of this specific isotope of Li. To show the potential of using this particular nuclide for probing dark matter interactions, we used the data collected previously by a CRESST prototype based on LiAlO_2 and operated in an above ground test-facility at Max-Planck-Institut für Physik in Munich, Germany. In particular, the inclusion of ^{6}Li in the limit calculation drastically improves the result obtained for spin-dependent interactions with neutrons in the whole mass range. The improvement is significant, greater than two order of magnitude for dark matter masses below 1 GeV/c^2, compared to the limit previously published with the same data.

Quasi-One-Dimensional Flow Modeling for Flight Environment Simulation System of Altitude Ground Test Facilities

The Flight Environment Simulation System (FESS) at Altitude Ground Test Facilities (AGTF) is used to test aircraft engines. The FESS model is the basis of research and verification of advanced control algorithms. To further improve the steady and dynamic accuracy of the FESS model, a modeling method based on quasi-one-dimensional flow is proposed. Firstly, based on the unified inlet/outlet boundary specifications, the component models of test equipment, such as the quasi-one-dimensional flow model of pipe, the regulating valve model considering the heat transfer process, the multi-inlet and multi-outlet volume model reflecting the mixing characteristics of air flow, and the air source model and engine model, were established. Secondly, according to the real structure and working mechanism of the FESS, the above component models were used to build the numerical simulation model of the FESS. The simulation results showed that the relative deviation of mass flow and pressure were less than 4.4% and 0.9%, respectively, which verifies the correctness of the modeling method. In addition, the PI controller was designed for the FESS, and the simulation results show that the model is able to support controller development and verification.

ВОЗДЕЙСТВИЕ ВУЛКАНИЧЕСКОГО ПЕПЛА НА АВИАЦИОННЫЕ ГАЗОТУРБИННЫЕ ДВИГАТЕЛИ

Volcanic ash clouds emitted into the Earth’s atmosphere by more than a thousand active volcanoes pose an immediate se-rious threat to flight safety, since volcanic ash particles in high concentrations can cause significant damage to aircraft. This article presents the consequences of an aircraft getting into a cloud of volcanic ash (damage to the fuselage and aer-odynamic surfaces of the aircraft, turbojet sustainer engines, antennas, air pressure and temperature receivers, other aircraft sys-tems), and also describes in detail the mechanisms and examples of the impact of volcanic ash on various types aircraft gas tur-bine engines. The global statistics of aircraft hitting volcanic ash clouds from 1935 to 2021 is given. The results of engineering tests of PW F100 bypass gas turbine engines under the influence of volcanic ash in the condi-tions of the scientific and CalspanTechnical Corporation, founded in 1943 in the United States of America, are considered. Also presented are the results of work under the VIPR (Vehicle Integrated Propulsion Research) program of the National Aerospace Agency of the United States of America (NASA) for a comprehensive study of the impact of volcanic ash on the F-117 (PW2040) power plant of the Boeing C-17 Globemaster III military transport aircraft. The results of research by the NASA national agency and the Calspan Corporation are compared with the main data of certification tests of the advanced PD-14 aircraft gas turbine engine developed by JSC «UEC-Aviadvigatel» in the conditions of the closed ground test facility Ts-17T of the FAA «CIAM named after P.I. Baranov» in accordance with the requirements of the European Aviation Safety Agency (EASA).

A Novel Boeing 737 Ground Test Facility for the Experimental Investigation of a Civil Aircraft Ecs

A Novel Boeing 737 Ground Test Facility for the Experimental Investigation of a Civil Aircraft Ecs

Thrust measurement and thrust balance development at DLR\u2019s electric propulsion test facility

Electric space propulsion thrusters only produce low thrust forces. For the fulfillment of a space mission this implies long thruster runtimes, and this entails long qualification times on ground. For such long testing times, a ground facility requires a vacuum chamber and a powerful pumping system which can guarantee high vacuum over extended times and under thruster gas load. DLR’s STG-ET is such a ground test facility. It has a high pumping capability for the noble gases typically used as propellants. One basic diagnostic tool is a thrust measurement device, among various other diagnostic systems required for electric propulsion testing, e.g. beam diagnostics. At DLR we operate a thrust balance developed by the company AST with a thrust measurement range of 250 mN and capable of thruster weights up to 40 kg. Adversely, it is a bulky and heavy device and all upgrades and qualification work needs to be done in a large vacuum chamber. In order to have a smaller device at hand a second thrust stand is under development at DLR. The idea is to have a light and compact balance that could also be placed in one of the smaller DLR vacuum chambers. Furthermore, the calibration is more robust and the whole device is equipped with a watercooled housing. First tests are promising and showed a resolution well below 1 mN. In this paper we give background information about the chamber, describe the basics of thrust measurement and the development of a new balance.

Localized time accurate sampling of nonequilibrium and unsteady hypersonic flows: methods and horizons

Modern “non-intrusive” optical methods are providing revolutionary capabilities for diagnostics of hypersonic flow fields. They generate accurate information on the performance of ground test facilities and provide local time accurate measurements of near-wall and off-body flow fields surrounding hypersonic test articles. They can follow the true molecular motion of the flow and detect nonequilibrium states and gas mixtures. They can be used to capture a wide range of turbulent scales and can produce highly accurate velocity, temperature and density measurements as well as time-frozen images that provide intuitive understanding of flow phenomena. Recent review articles address many of these methods and their applications. The methods highlighted in this review are those that have been enabled or greatly improved by new, versatile laser systems, particularly including kHz rate femtosecond lasers and MHz rate pulse burst lasers. Although these methods can be applied to combusting environments, the focus of this review is on external high Mach number flows surrounding test articles and wind tunnel core flow properties. The high repetition rates enable rapid time evolving flows to be analyzed and enable the collection of large data sets necessary for statistical analysis. Future capabilities based on the use of atomic vapor filters and on frequency tunable, injection locked MHz rate lasers are promising.

Time-synchronized laser-induced fluorescence in the near-field of a 600 Watt Hall thruster

We report on the results of an experimental campaign to measure time-varying velocity distributions in the near-field of a low power Hall thruster. We employ a sample-hold technique, enhanced by parallelizing the measurement hardware into several signal processing channels that vastly increases the data acquisition rate. The measurements are applied to study flow field dynamics in a commercial BHT-600 Hall thruster undergoing unforced breathing mode oscillations in the 44–49 kHz range. A very detailed experimental picture of the near-field emerges from these studies. The results indicate that velocity fluctuations lessen further downstream of the exit plane. Along the thruster axis where there is a general appearance of a central jet, there is evidence of a low velocity ion population in between the periodic bursts of high velocity ions, indicative of local ionization of neutrals outside of the thruster. One possible source of this residual ionization may be background chamber gas, which is not unexpected with the limited pumping capacity of ground test facilities.

Development and commissioning of the T6 Stalker Tunnel

The T6 Stalker Tunnel is a multi-mode, high-enthalpy, transient ground test facility. It is the first of its type in the UK. The facility combines the original free-piston driver from the T3 Shock Tunnel with modified barrels from the Oxford Gun Tunnel. Depending on test requirements, it can operate as a shock tube, reflected shock tunnel or expansion tube. Commissioning tests of the free-piston driver are discussed, including the development of four baseline driver conditions using piston masses of either 36 kg or 89 kg. Experimental data are presented for each operating mode, with comparison made to numerical simulations. In general, high-quality test flows are observed. The calculated enthalpy range of the experimental conditions achieved varies from 2.7hbox { MJ kg}^{-1} to 115.0hbox { MJ kg}^{-1}.Graphical abstract

Morphological Evolution of Ordinary Chondrite Microstructure during Heating: Implications for Atmospheric Entry

Abstract Meteoroid entry physics remain poorly understood, owing to the extreme conditions experienced by the meteoroid during hypervelocity atmospheric passage, which are not reproducible in ground-test facilities. Therefore, much of our knowledge of fundamental processes is based on bolide lightcurve inference and a posteriori analysis of recovered meteorites. Here, novel in situ microtomography experiments at entry-relevant temperatures were performed on samples of two ordinary chondrites: Tamdakht (H5) and Tenham (L6). The two meteorites were imaged while undergoing a temperature ramp from room temperature to 1200°C. A machine-learning mediated analysis of the microstructural evolution reveals incongruent melting of the meteorite, initiated by the meteoritic iron and iron sulfide grains, and subsequent flow through microcracks that leads to the evolution of large voids. This behavior is correlated to a broad, high-temperature endotherm, noted from differential scanning calorimetry analysis, indicative of the heat of fusion of the melting grains. Correspondingly, a surface elemental analysis indicates that the sulfur species in iron sulfide are highly mobile, which can result in the formation of nonstoichiometric iron–sulfur compounds with melting points that span the temperature range of the observed endotherm. The implications for entry phenomena, in particular meteoroid ablation, are discussed.